1. Field of the Invention
The present invention relates to a lens distance-varying mechanism for varying the distance between two lens groups, and a step-zoom lens which incorporates such a mechanism.
2. Description of the Related Art
The assignee of the present invention has proposed a step-zoom lens system having a distance-varying lens group in which the distance between two lens groups varies at an intermediate focal length. Specifically, this zoom lens system includes a plurality of movable lens groups which are moved to vary the focal length of the zoom lens system, and at least one lens group of the plurality of movable lens groups includes two sub-lens groups serving as a switching lens group. One of the two sub-lens groups is moveable, along the optical axis of the zoom lens system, to be selectively positioned at one of the movement extremities of the moveable sub-lens group with respect to the other sub-lens group. In a short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the moveable sub-lens group is arranged to position at one of the movement extremities thereof. In a long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the moveable sub-lens group is arranged to position at the other of the movement extremities thereof. The moving path of the switching lens group having the two sub-lens groups, and the moving paths of the other lens groups of the plurality of movable lens groups are discontinued at the intermediate focal length. The zoom lens system is arranged to form an image on a predetermined image plane in accordance with a position of the moveable sub-lens group. This zoom lens system is disclosed in U.S. Pat. No. 6,369,955 (Japanese Unexamined Patent Publication No. 2000-275518).
To apply this step-zoom lens system, the distance between two sub-lens groups of a lens group must be varied at an intermediate focal length.